Research On Residual Stresses In Girth Welding Joint Of The Layered Vessel

Layered wrapped structure is one kind of pressurized equipment in high pressure vessels. Layered vessels are used widely in chemical industries. The distribution of residual stresses in girth welding joint of layered vessels is very complicated, and it is hard to detect by using nondestructive testing. The residual stresses are generated and influence the structure integrity. And the residual stresses can influence the ability of bearing loads and the safety of the vessel. It is an important subject to ensure the safety of the vessel when it is running.By using ABAQUS, 2D axisymmetric finite element model of the layered-to-layered weld joint is created and simulated. The sequential coupling finite element procedure and birth-death element method are applied to analyze the 70mm-thick tube joint welding residual stresses. The residual stresses in the weld zone, heat affected zone, inner surface and outer surface of the vessel have been discussed.This paper discussed three different layer structure finite element models, including joint of single layer model, single head to layered shell model and layered-to-layered shell model, and the differences of the residual stresses distribution have been discussed. The calculated results show that discrete layered structure has optimized the residual stress along inner surface, and using this layer structure has advantages to bearing loads.Moreover, radial and axial and hoop residual stress are plotted for weld process parameters such as weld passes, heat input, preheating temperature, welding sequence, gap between discrete layers and surfacing welding method, and the differences are discussed. The calculated results show that the more weld passes the better distribution of the residual stresses; and the bigger heat input the worse distribution of the residual stresses along heat affected zone; and preheating temperature welding sequence and gap between discrete layers have little impact on the residual stresses. Using surfacing welding method can reduce the defect in the layered gap and optimize the distribution of the residual stresses.Through this study some advices have been put forward to control the residual stresses. Using surfacing welding, with small heat input, low preheating temperature and multi-passes is better than other welding methods. Moreover, using reasonable welding sequence and avoiding too large gap between discrete layers also have been advised. And by taking the advantages of layered vessels can ensure process safety.